Cutting tool with retainer having controlled hardness

ABSTRACT

The present invention provides a rotatable cutting tool with a bit, a washer, and a retainer. The retainer surrounds at least a portion of the shank of the bit. Wear on the shank is reduced by providing a retainer with a controlled hardness that is less than the hardness of the shank of the bit, while still allowing similar wear on the retainer.

FIELD OF THE INVENTION

The present invention relates to rotatable cutting tools, and moreparticularly retainers for rotatable cutting tools having controlledhardness.

BACKGROUND INFORMATION

Rotatable cutting tools are used in a variety of applications and areoften used in road milling operations. The rotatable cutting tools ofteninclude a bit, a washer, and a retainer. The bit often includes a shank.A retainer is placed around the shank of the bit in order to retain thetool in the holder during operation and protect the holder from wear dueto the rotation of the cutting tool. Many technological developmentshave increased the life of the rotatable cutting tool bits. As the lifeof the bits have increased, the shank of the rotatable cutting tool bitscan become the limiting factor in the life of the bit due to wearexperience by the shank during operation of the bit. Several attemptshave been made to increase the life of the shank, including bodycoatings of the shank and plasma transferred arc (PTA) hard-facing ofthe shank. However, the body coatings do not last long enough and thePTA hard-facing decreases the life of the retainers due to wear anddecreases the shank fatigue life. There is a need to increase the lifeof the shank while also not decreasing the life of the retainers.

SUMMARY OF THE INVENTION

The present invention provides rotatable cutting tools with bits andretainers. The retainers surround at least a portion of a shank of thebit. The hardness of the retainers is controlled to selected levels lessthan the hardness of the shank of the bit. Cutting tools of the presentinvention address the issues mentioned above by providing cutting toolswith retainers having controlled lower hardness than the shank of thecutting tool bit.

An aspect of the present invention is to provide a cutting toolcomprising a shank comprising a shank outer surface and a retainercomprising a retainer inner surface at least partially surrounding theshank outer surface. The retainer has a controlled hardness less than ahardness of the shank selected to reduce wear between the shank outersurface and the retainer inner surface.

Another aspect of the present invention is to provide a method ofassembling a cutting tool, comprising installing a low hardness retaineraround a cutting tool bit shank, wherein the low hardness retainercomprises an inner surface at least partially surrounding an outersurface of the bit shank, and the inner surface has a controlledhardness less than a hardness of the bit shank selected to reduce wearbetween the bit shank outer surface and the low hardness retainer innersurface.

These and other aspects of the present invention will be more apparentfrom the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a rotatable cutting tool with a retainerand washer in accordance with an embodiment of the present invention.

FIG. 2 is a side view of the rotatable cutting tool of FIG. 1 .

FIG. 3 is a cross-sectional side view taken through section 3-3 of FIG.2 .

FIG. 4 is an isometric view of a retainer in accordance with anembodiment of the present invention.

FIG. 5 is an end view of the retainer of FIG. 4 .

FIG. 6 is a graph of rotatable cutting tool shank material loss forstandard retainers and retainers of the present invention having lowerhardness, showing significantly decreased wear rates for the rotatablecutting tool shanks used with the low-hardness retainers of the presentinvention.

FIG. 7 is a graph of rotatable cutting tool retainer material loss forstandard retainers and retainers of the present invention having lowerhardness, showing roughly similar wear rates for the low-hardnessretainers of the present invention.

DETAILED DESCRIPTION

FIGS. 1-3 illustrate a rotatable cutting tool 100 with a retainer 200and a washer 300 in accordance with an embodiment of the invention. Therotatable cutting tool 100 includes a cutting tip 120 arranged at afirst end of the rotatable cutting tool 100. The cutting tip 120 may bemade of standard materials such as tungsten carbide, polycrystallinediamond, or other material structured and arranged for cutting hardmaterials such as asphalt. The cutting tip 120 may be uncoated orcoated. The cutting tip 120 is secured to a bolster 130. The bolster 130may be centered around a longitudinal axis 500, extending centrallyalong the length of the cutting tool 100. The bolster 130 is secured toa bit body 150 that is surrounded by a bit collar 140. A bit shank 160extends in a rearward direction from the bit body 150. The retainer 200may be arranged on the outside of the bit shank 160.

Two different orientations of the washer 300 are illustrated in FIGS.1-3 . The initial location of the washer 300 is where the washer 300 islocated before installation of the cutting tool 100 into a holder (notshown). In the initial location, the washer 300 is arranged around theoutside of the retainer 200 such that the retainer 200 is in contactwith the washer 300. The final location of the washer 300′ is where thewasher 300′ is located after the cutting tool 100 is installed into theholder. In the final location, the washer 300′ is in contact with thebit body 150 of the rotatable cutting tool 100.

The bit shank 160 may be cylindrical in shape. The bit shank 160 mayhave a shank length Ls measured along the longitudinal axis 500 that isat least 1.00 inches, for example, at least 1.20 inches or at least 1.40inches. The shank length Ls may be at most 2.50 inches, for example, atmost 1.70 inches or at most 1.50 inches. The shank length Ls may rangefrom 1.00 inches to 2.50 inches, for example from 1.40 inches to 1.50inches. The bit shank 160 may have an outer diameter Ds of at least 0.40inches, for example, at least 0.60 inches or at least 0.65 inches. Thebit shank 160 may have an outer diameter Ds of at most 1.20 inches, forexample at most 0.80 inches or at most 0.67 inches. The bit shank 160outer diameter Ds may range from 0.4 inches to 1.20 inches, for example,from 0.6 inches to 0.8 inches or from 0.65 inches to 0.67 inches.

The retainer 200, as shown in FIGS. 1-5 , may be structured and arrangedto surround at least a portion of the outer surface 162 of the bit shank160 having the outer diameter Ds. The retainer 200 has a generallycylindrical outer surface 210. The retainer 200 has an inner surface 220having an inner diameter D_(R) that may be greater than or equal to theouter diameter Ds of the bit shank 160. When the cutting tool 100 andretainer 200 are installed in a standard holder (not shown), theretainer 200 expands radially outward such that its outer surface 210contacts and is retained in a central bore of the holder to therebyreduce or eliminate relative rotation between the retainer 200 and theholder. The inner diameter D_(R) Correlates to the inner diameter D_(R)of the retainer 200 when the washer 300′ is in the final position afterinstallation of the rotatable cutting tool 100 into the holder.

The retainer inner diameter D_(R), when installed in a holder, may be atleast 0.40 inches, for example, at least 0.60 inches or at least 0.67inches. The retainer 200 may have an inner diameter D_(R) of at most1.40 inches, for example, at most 0.90 inches or at most 0.69 inches.The retainer inner diameter D_(R) may range from 0.40 inches to 1.40inches, for example, from 0.60 inches to 0.90 inches or from 0.67 inchesto 0.69 inches.

When the rotatable cutting tool 100 is installed in a holder, and thewasher 300′ is in the final position, there may be an average installedgap between the retainer inner surface 220 and the shank outer surface162. The installed gap may vary after installation as the shank mayshift during operation, causing some portions of the shank outer surface162 to be closer to the retainer inner surface 220 than other portionsof the shank outer surface 162. The installed gap may equal half of thedifference between the retainer inner diameter D_(R) and the shank outerdiameter Ds when the rotatable cutting tool 100 is in the installedposition. The installed gap may be at least 0.001 inches, for example,at least 0.003 inches or at least 0.005 inches. The installed gap may beat most 0.100 inches, for example, at most 0.050 inches or at most 0.020inches. The installed gap may range from 0.001 inches to 0.100 inches,for example, from 0.003 inches to 0.050 inches or from 0.005 inches to0.020 inches.

When surrounding at least a portion of the outer diameter Ds of the bitshank 160, the retainer 200 may extend along at least a portion of theshank length Ls. The length of the retainer L_(R) may be less than,equal to, or greater than the shank length Ls. The retainer 200 may havea retainer length L_(R) that is at least 1.0 inches, for example, atleast 1.4 inches or at least 1.45 inches. The retainer length L_(R) maybe at most 2.0 inches, for example, at most 1.6 inches or at most 1.55inches. The retainer length L_(R) may range from 1.0 inches to 2.0inches, for example from 1.45 inches to 1.55 inches.

The retainer 200 includes a retainer gap 230 extending axially along thelength of the retainer in a direction parallel with the longitudinalaxis 500 from the retainer outer surface 210 to the retainer innersurface 220. The retainer gap 230 may be defined by a gap angle A_(G).

The retainer 200 may include at least one retainer indent 240, forexample two, three, or four retainer indents 240, structured andarranged on the retainer inner surface 220. The retainer indent 240 mayextend radially inward from the retainer inner surface 220. The retainerindent 240 may include a curved indent inner surface 242, a flat indentrear surface 244, and an angled or rounded indent front surface 246.

The bit shank 160 may include a radially inwardly extending shank groove164 for a portion of the shank length Ls away from the bit shank bottomsurface 170. The shank groove 164 may have a groove outer diameter DGthat is smaller than the shank diameter Ds. The shank groove 164 may bestructured and arranged to receive the at least one retainer indent 240.The flat indent rear surface 244 may be structured and arranged toengage the shank groove 164. The flat indent rear surface 244 may engagewith the shank groove lower edge 168 when installed around the bit shank160 such that it prevents the retainer 200 from moving behind the shankgroove 164 after installation.

When the washer 300′ is in the final location against the bit body 150,and the retainer 200 expands, coming in contact with the bore of theholder, relative axial movement between the retainer 200 and the bitshank 160 is prevented while still allowing rotational movement betweenthe bit shank 160 and the retainer 200. Axial movement is prevented bythe flat indent rear surface 244 that comes in contact with the shankgroove lower edge 168 when the bit shank 160 attempts to move in theforward axial direction. During rotational movement of the bit shank 160in the retainer 200, the shank groove 164 may freely move around theretainer indent 240, allowing the bit shank 160 to rotate within theretainer 200. Therefore, during operation of the rotatable cutting tool100, the shank 160 may rotate within the retainer 200 while the retainer200 prevents the bit shank 160 from moving in the axial direction (e.g.,forward relative to the retainer 200).

During operation of the rotatable cutting tool 100, the retainer innersurface 220 may engage with the outer surface 162 of the bit shank 160,causing wear. A retainer 200 may usually be made of spring steel with ahardness in the range of 47 to 50 Rockwell Hardness Scale C (HRC) whilea bit shank 160 is generally made of steel with a hardness in the rangeof 45-50 HRC. HRC values may be measured using the standard methoddescribed in ASTM standard E0018-20.

In accordance with the present invention, having a retainer 200 with acontrolled hardness that is substantially less than the hardness of thebit shank 160 has been found to result in decreased wear of the bitshank 160, as well as minimizing wear of the softer retainer. Inconventional pairings of retainers and bit shanks, the hardness of theshanks and retainers are about the same, for example, the hardness ofthe retainer is in the range of 47 to 50 HRC and the hardness of the bitshank is in the range of 45-50 HRC. However, when the hardness of thebit shank 160 remains in the range of 45 to 50 HRC, for example 47 to 50HRC, and the hardness of the retainer 200 is decreased to a range of 38to 44 HRC, for example 39 to 43 HRC or 40 to 42 HRC, then the wear ofthe bit shank 160 is minimized while also resulting in minimal wear ofthe retainer 200. The wear of the retainer 200 with a hardness in therange of 38 to 44 HRC, 39 to 43 HRC, or 40 to 42 HRC may be similar tothe wear experienced by a retainer 200 with a hardness in the range of47 to 50 HRC when the bit shank 160 has a hardness in the range of 45-50HRC. Generally, it would be expected that a decrease in hardness of theretainer 200 would result in increased wear on the retainer 200.However, with these hardness values for the retainer 200 and the bitshank 160, it has been seen that a lower hardness of the retainer 200can still result in a significant decrease in wear of the bit shank 160without sacrificing significant additional wear on the retainer 200.

As used herein, the terms “low hardness” and “lower hardness” whenreferring to the retainer 200 means the retainer 200 has a controlledhardness less than the hardness of the bit shank 160 in which theretainer 200 is installed. In some non-limiting embodiments or aspects,the bit shank 160 may be at least 1 HRC harder than the retainer 200,for example, at least 2 HRC, at least 3 HRC, at least 4 HRC, at least 5HRC, at least 8 HRC, or at least 11 HRC harder than the retainer 200.The bit shank 160 may range from 2 to 11 HRC harder than the retainer200, for example, from 4 to 9 HRC harder or from 6 to 7 HRC harder thanthe retainer 200.

The hardness of the retainer 200 may be decreased by tempering and/orheat treating the retainer 200 at elevated temperatures and selectedtimes, which can be determined by those skilled in the art without undueexperimentation. The tempering of the retainer 200 may occur afterinitial hardening of the retainer 200. A retainer 200 may be temperedonce, twice, or more in order to obtain the desired hardness.

In some non-limiting embodiments or aspects, the retainer 200 mayinclude a steel, such as a spring steel. For example, the retainer 200may include 1070 grade spring steel, or other spring steals, such as1050, 1060, 65Mn, and/or the like. The 1070 grade spring steel mayinclude carbon in the range of 0.65%-0.75% by weight and manganese inthe range of 0.60%-0.90% by weight. The 1070 grade spring steel may alsoinclude sulfur in the range of 0% to 0.050% by weight and/or phosphorousin the range of 0% to 0.040% by weight. A majority of the balance of thecomposition by weight may include iron. The bit shank 160 may includeknown steels, such as 4140, and/or the like.

In some non-limiting embodiments or aspects, the retainer 200 mayinclude 65Mn steel. The 65Mn steel may include carbon in the range of0.62% to 0.70% by weight, silicon in the range of 0.17% to 0.37% byweight, manganese in the range of 0.90% to 1.20% by weight, phosphorousin the range of 0% to 0.035% by weight, and sulfur about in the range of0% to 0.035% by weight. The 65Mn steel may also include chromium in therange of 0%-0.25% by weight, nickel in the range of 0%-0.25% by weight,and/or copper in the range of 0%-0.25% by weight. A majority of thebalance of the composition by weight may include iron.

The retainer 200 may be made of the same or a different material thanthe bit shank 160. The bit shank 160 may be made of the same ordifferent material than the bit body 150. The retainer 200 may becomposed entirely or mostly of a spring steel, such as 1070 grade springsteel or 65Mn steel. The retainer 200 may have a majority of thecomposition having the same hardness. At least 85% of the retainer 200may have hardness in the range of 39 to 43 HRC, for example, at least90% or at least 95% of the retainer may have a hardness in the range of39 to 43 HRC. The retainer 200 may be able to achieve the hardness of 39to 43 HRC without the use of any cladding, coating, and/or hard facingof the retainer inner surface 220. In some non-limiting embodiments oraspects, the entire cross-sectional area of the retainer 200 may be aconstant hardness, e.g., the same hardness. The entire cross-sectionalarea of the bit shank 160 may be a constant hardness, e.g., the samehardness.

A radial thickness of the retainer 200 may be defined between theretainer outer surface 210 and the retainer inner surface 220. Thehardness of the retainer 200 may be substantially constant throughoutthe radial thickness of the retainer 200 in the radial direction. Aradial thickness of the bit shank 160 may be defined by the shank outersurface 162. The hardness of the shank 162 may be substantially constantthroughout the radial thickness of the bit shank 160.

Illustrating the invention is the following example that is not to beconstrued as limiting the invention to their details.

Example

Bit shank and retainer hardness, as well as wear characteristics, weremeasured on assemblies including standard bit shanks and standardretainers, in comparison with standard bit shanks and lower hardnessretainers of the present invention. In addition, retainer wearcharacteristics were measured on assemblies including standard retainersand bit shanks having PTA hard-facing.

Hardness Testing

In all retainer sets, the bit shanks of the standard retainer sets weremade of 4140 type steel. In the case of the PTA hard-facing bit shanks,the 4140 type steel was coated with a standard PTA hard-facing material.The hardness values of the standard bit shanks (without PTA hard-facing)were measured to be between 45 and 50 HRC, measured by ASTM standardE0018-20.

In all retainer sets, the retainers were made of 1070 spring steel. Thestandard retainers had hardness values measured to be between 47 and 50HRC, measured by ASTM standard E0018-20. The lower hardness retainerswere produced by tempering standard hardened retainers at elevatedtemperatures for sufficient time to reduce hardness to desired levels ofbetween 39 and 43 HRC.

Wear Testing

Wear tests were conducted for assemblies with standard shanks andstandard retainers, standard shanks and lower hardness retainers, andPTA hard-facing shanks and standard retainers. Approximately 60rotatable cutting tools for each of the different types of assemblies,totaling 180 rotatable cutting tools, were installed into holders whichwere attached to blocks on a rotating cutting drum installed in astandard road milling machine. The blocks were arranged in a 15millimeter spacing pattern as commonly used in the road constructionindustry. The machine, equipped with rotatable cutting tools includingtools of standard retainers, tools with lower hardness retainers, andtools with hard facing on the shank with standard retainers, was thenrun for 4 days milling approximately 2 inches of asphalt from the roadsurface. Each day the machine was run for approximately 9 hours. Duringoperation the cutting drum rotated at approximately 110 rpm and coolwater was constantly sprayed on the tools as the drum rotated. Thecutting speed of the machine was approximately 115 feet per minute. Atthe end of the four days all of the tools were removed from the holdersand the wear of the shanks and retainers on a portion of the tools wasmeasured. The total asphalt cut was 43,579 yd².

The standard and lower hardness retainer sets were measured to determinethe amount of wear of the components. The measurement of the amount ofwear was conducted by measuring diameters of the bit shanks before andafter milling, and by measuring radial thicknesses of the standardretainers and lower hardness retainers before and after milling, usingstandard measuring equipment such as digital calipers and micrometers.For the bit shanks, wear testing was conducted at the upper portions andthe lower portions of the bit shanks. The amount of wear is measured interms of inches of material removed from the outer diameters of the bitshanks and inner diameters of the retainers.

Results of the wear testing are shown in FIGS. 6 and 7 . As can be seenin FIG. 6 , having a retainer with a hardness that is less than the bitshank results in decreased wear of the bit shank. When the hardness ofthe retainer is between 47-50 HRC and the hardness of the bit shank isbetween 45-50 HRC, the average wear of the upper portion of the bitshank is 0.021 inches of material loss after the 4 days of testing. Theaverage wear of the lower portion of the bit shank is about 0.0134inches of material loss after the 4 days of testing.

When the average hardness of the shank is between 45-50 HRC and theaverage hardness of the retainer is decreased to between 39-43 HRC, theaverage wear of the upper portion of the bit shank is 0.0154 inches ofmaterial loss after the 4 days of testing. The average wear of the lowerportion of the bit shank is about 0.0084 inches of material loss afterthe 4 days of testing.

As can be seen in FIG. 7 , having the lower hardness of the retainerresults in a similar amount of wear of the retainer compared to astandard retainer. When the hardness of the standard retainer is between47-50 HRC and the hardness of the bit shank is between 45-50 HRC, theaverage wear of the retainer is 0.0116 inches of material loss perretainer after the 4 days of testing. When the average hardness of theshank is between 45-50 HRC and the average hardness of the retainer isdecreased to between 39-43 HRC, the average wear of the lower hardnessretainer is 0.0118 inches of material loss per retainer after the 4 daysof testing.

Also shown in FIG. 7 is the average wear of a standard retainer whenused with the wear protected shank (i.e., the PTA hard-faced shank). Theaverage wear of the standard retainer was 0.0280 inches of material lossper retainer after 4 days of testing.

The data in this example demonstrate that when the hardness of theretainer is decreased from 47-50 HRC to 39-43 HRC, average shank wear isdecreased both in the upper portion and the lower portion of the bitshank. However, the average wear of the retainer remains about the samedespite the decrease in the retainer hardness. The data alsodemonstrates that using wear protection on the shank with a standardretainer causes a significant increase in material loss of the retainer,thus causing a significant decrease in the life of the retainers.

As used herein, “including,” “containing” and like terms are understoodin the context of this application to be synonymous with “comprising”and are therefore open-ended and do not exclude the presence ofadditional undescribed or unrecited elements, materials, phases ormethod steps. As used herein, “consisting of” is understood in thecontext of this application to exclude the presence of any unspecifiedelement, material, phase or method step. As used herein, “consistingessentially of” is understood in the context of this application toinclude the specified elements, materials, phases, or method steps,where applicable, and to also include any unspecified elements,materials, phases, or method steps that do not materially affect thebasic or novel characteristics of the invention.

For purposes of the description above, it is to be understood that theinvention may assume various alternative variations and step sequencesexcept where expressly specified to the contrary. Moreover, all numbersexpressing, for example, quantities of ingredients used in thespecification and claims, are to be understood as being modified in allinstances by the term “about”. Accordingly, unless indicated to thecontrary, the numerical parameters set forth are approximations that mayvary depending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents, each numerical parametershould at least be construed in light of the number of reportedsignificant digits and by applying ordinary rounding techniques.

It should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

In this application, the use of the singular includes the plural andplural encompasses singular, unless specifically stated otherwise. Inaddition, in this application, the use of “or” means “and/or” unlessspecifically stated otherwise, even though “and/or” may be explicitlyused in certain instances. In this application, the articles “a,” “an,”and “the” include plural referents unless expressly and unequivocallylimited to one referent.

In this application, the use of “horizontal”, “vertical”, “positive” and“negative” are used as relative terms and it is understood that duringuse the d rotatable cutting tool may have different orientations.

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the invention as defined inthe appended claims.

What is claimed is:
 1. A cutting tool comprising: a bit shank comprisinga bit shank outer surface; and a retainer comprising a retainer innersurface at least partially surrounding the bit shank outer surface,wherein the retainer has a controlled hardness less than a hardness ofthe bit shank selected to reduce wear between the bit shank outersurface and the retainer inner surface.
 2. The cutting tool of claim 1,wherein the hardness of the bit shank outer surface is at least 2 HRCgreater than the hardness of the retainer inner surface.
 3. The cuttingtool of claim 1, wherein the hardness of the bit shank outer surface isat least 4 HRC greater than the hardness of the retainer inner surface.4. The cutting tool of claim 1, wherein the hardness of the bit shankouter surface is greater than 45 HRC, and the hardness of the retainerinner surface is less than 45 HRC.
 5. The cutting tool of claim 1,wherein the hardness of the retainer inner surface is at most 43 HRC. 6.The cutting tool of claim 1, wherein the bit shank comprises 4140 typesteel.
 7. The cutting tool of claim 1, wherein the retainer comprises1070 grade spring steel or 65Mn steel.
 8. The cutting tool of claim 1,wherein the bit shank outer surface does not include a coating or hardfacing.
 9. The cutting tool of claim 1, wherein the retainer innersurface does not include a coating or hard facing.
 10. The cutting toolof claim 1, wherein the retainer comprises a retainer radial thicknessdefined between the retainer inner surface and a retainer outer surface,the retainer radial thickness having a substantially constant retainerhardness throughout the retainer radial thickness in a radial direction.11. The cutting tool of claim 1, wherein the bit shank comprises aradial thickness defined by the bit shank outer diameter, the bit shankradial thickness having a substantially constant bit shank hardnessthroughout the bit shank radial thickness in a radial direction.
 12. Amethod of assembling a cutting tool, comprising installing a lowhardness retainer around a cutting tool bit shank, wherein the lowhardness retainer comprises an inner surface at least partiallysurrounding an outer surface of the bit shank, and the inner surface hasa controlled hardness less than a hardness of the bit shank selected toreduce wear between the bit shank outer surface and the low hardnessretainer inner surface.
 13. The method of claim 12, wherein the retainercomprises spring steel.
 14. The method of claim 13, wherein the springsteel comprises a 1070, 1050, 1060 or 65Mn grade spring steel.
 15. Themethod of claim 12, wherein the hardness of the bit shank outer surfaceis at least 2 HRC greater than the hardness of the retainer innersurface.
 16. The method of claim 12, wherein the hardness of the bitshank outer surface is at least 4 HRC greater than the hardness of theretainer inner surface.
 17. The method of claim 12, wherein the hardnessof the bit shank outer surface is at least 45 HRC.
 18. The method ofclaim 12, wherein the hardness of the retainer inner surface is at most43 HRC.